1. Field of the Invention
This invention relates to a group of compounds classified in the field of organic chemistry as furopyridinones and furopyazinones useful as color formers in pressure-sensitive carbonless duplicating systems and thermal marking systems, to processes for the preparation thereof and to pressure-sensitive duplicating systems and thermal marking systems containing the same.
2. Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as color formers for carbonless duplicating systems. Among the more widely recognized classes are phenothiazines, for example, benzoyl leuco methylene blue; fluorans, for example, 2'-anilino-6'-diethylaminofluoran; phthalides, for example, crystal violet lactone, and various other types of color formers currently employed in commercially acceptable carbonless duplicating systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289 which issued July 5, 1955, July 23, 1957 and June 26, 1962, respectively. Many of the color formers in the prior art, however, suffer one or more disadvantages such as low tinctorial strength, poor light stability, low resistance to sublimation and low solubility in common organic solvents.
The following appears to constitute the most pertinent prior art relative to the present invention.
U.S. Pat. No. 3,775,424, issued Nov. 27, 1973, discloses in most pertinent part a series of compounds reportedly employed in pressure-sensitive record material and mark-forming mainfold systems and having the formula ##STR1## wherein inter alia each X is ##STR2## and each R is hydrogen, an alkyl radical having 1 to 4 carbon atoms, an alkoxy radical having 1 to 4 carbon atoms or a phenyl radical.
Belgian Pat. No. 812,406 published July 1, 1974 discloses in most pertinent part a pressure-sensitive copying paper containing as a color former a compound having the formula ##STR3## or a mixture thereof wherein inter alia Y is hydrogen and one of A and A' is indolyl and the other is a nitrogen or sulfur containing heterocyclic group.
3. Prior Publications
Belgian Pat. No. 862,217, published June 22, 1978, which corresponds essentially to pending U.S. patent applications Ser. Nos. 821,926 and 942,996, filed Aug. 4, 1977 and Sept. 18, 1978, respectively, in the names of Paul Joseph Schmidt and William Mo-Wei Hung, the inventors in the instant application, discloses a series of phthalides useful as color formers in pressure-sensitive carbonless duplicating systems, thermal marking systems and hectographic or spirit-reproducing copying systems and having the formula ##STR4## wherein: Q is di-lower-alkylamino, nitro, halo or COX, where X is hydroxyl, benzyloxy, alkoxy having from 1 to 18 carbon atoms or OM where M is an alkali metal cation, an ammonium cation or a mono-, di- or tri-alkylammonium cation having from 1 to 18 carbon atoms;
n is 0; or 1 when Q is di-lower-alkylamino, nitro or COX; or from 1 to 4 when Q is halo; PA1 Y.sub.1, Y.sub.2, Y.sub.3 and Y.sub.4 are the same or different and are hydrogen, halo, hydroxyl, lower-alkoxy, alkyl having from 1 to 9 carbon atoms, phenyl-lower-alkyl, COOR.sub.4 or NR.sub.5 R.sub.6, where R.sub.4 and R.sub.5 are hydrogen or lower-alkyl and R.sub.6 is hydrogen, lower-alkyl, cycloalkyl having from 5 to 7 carbon atoms or lower alkanoyl; Z is ##STR5## in which: R is hydrogen or non-tertiary alkyl having from 1 to 4 carbon atoms; PA1 R.sub.1 is hydrogen, or non-tertiary alkyl having from 1 to 18 carbon atoms; PA1 R.sub.2 is hydrogen, phenyl or non-tertiary alkyl having from 1 to 4 carbon atoms; PA1 R.sub.3 is hydrogen, non-tertiary alkyl having from 1 to 4 carbon atoms or non-tertiary alkoxy having from 1 to 4 carbon atoms; PA1 R.sub.7 is hydrogen, halo, lower-alkyl, lower-alkoxy or dilower-alkylamino; PA1 R.sub.8 is lower-alkyl; and PA1 R.sub.9 is lower-alkyl, benzyl, phenyl or phenyl substituted with a lower-alkyl or lower-alkoxy group. PA1 R.sub.4 is lower alkyl; PA1 R.sub.5 is lower alkyl or benzyl; PA1 R.sub.6 is hydrogen or non-tertiary alkyl having from 1 to 18 carbon atoms; and PA1 R.sub.7 is hydrogen, phenyl or non-tertiary lower alkyl. PA1 5-[4-(dimethylamino)phenyl]-5-(diphenylamino)furo-[3,4-b]pyridine-7(5H)-one PA1 A is ##STR13## and Z is ##STR14## PA1 A is ##STR18## with an aniline of Formula VI or an indole of Formula VII can produce isomers or a mixture of isomers of Z-CO-pyridinecarboxylic acids (Formula II). For example, reaction of 2,3-pyridinedicarboxylic anhydride (Formula Va hereinbelow) with an aniline or an indole of Formula VI or VII respectively (Z--H hereinbelow) can produce either a 2-(Z--CO)-3-pyridinecarboxylic acid (Formula IIa) or a 3-(Z--CO)-2-pyridinecarboxylic acid (Formula IIb) or a mixture of these. It will, of course, be appreciated that the ratio of isomers obtained will depend on various reaction conditions such as temperature, solvent, catalyst and the relative solubility of the isomers in the reaction medium. Ordinarily, when carried out as described herein the reaction produces a mixture of isomers with the 2-(Z--CO)-3-pyridinecarboxylic acid (Formula IIa) predominating in the isolated product. If desired, the mixture of isomeric Z--CO--pyridinecarboxylic acids can be separated by conventional means such as selective precipitation at different pH, fractional crystallization or chromatography and each of the individual isomers IIa and IIb can then be reacted with an appropriate diarylamine of Formula III to produce a furo-[3,4-b]pyridine-5(7H)-one of Formula Ia and a furo[3,4-b]pyridine-7(5H)-one of Formula Ib, respectively. It is generally preferred however, to simply react the isolated mixture of isomeric Z--CO-pyridinecarboxylic acids of Formulas IIa and IIb with a diarylamine to produce an isomer mixture of furopyridinones of Formulas Ia and Ib which can be separated by conventional means if desired. However, since both isomers are useful as color formers it is economically advantageous to simply use the isolated mixture thereof in the practice of this invention. ##STR19##